This invention relates to the transfer of solutes and fluids across porous membranes, and more particularly to the precision control of such transfer. These porous membranes are frequently referred to as semipermeable membranes and, as a class, are per se well known in the art.
The transfer of solutes across porous membranes by diffusion is known as dialysis. Ultrafiltration is a separation process in which large molecules or colloidal particles are physically restrained from passing through a porous membrane with the solvent and smaller solutes which do pass through the membrane.
Dialysis and ultrafiltration have important commercial and medicinal applications. They are also widely used in chemical processing to recover and isolate certain constituents. An important medical usage is in the removal of waste materials and fluids when there has been a failure or impairment of function of the human kidney.
The use of dialysis and ultrafiltration in lieu of or in supplement to the kidney function involves the use of an artificial kidney (dialyzer) through which blood from the patient is circulated on one side of a semipermeable membrane, with a cleansing fluid, known as the dialysate, circulating on the other side. Since the process involves the transfer of wastes or excess fluids from the blood to the dialysate, it is known as hemodialysis, with the fluid removed from the blood being known as the ultrafiltrate.
Hemodialysis can take place only as long as there is a concentration gradient between the waste particles in the blood and those present in the dialysate.
In addition to the dialysis, it is important for the ultrafiltration to be controllable with precision. If too little or too much waste fluid is removed from the patient there can be adverse effects such as hypertension or hypotension.
Accordingly, it is an object of the invention to facilitate the control or ultrafiltration. A related object is to facilitate the control of hemodialysis and the removal of waste fluid from the blood by ultrafiltration.
A further object of the invention is to facilitate the change of dialysis liquid without the complete or substantially complete termination of the dialysis process.